Transcript for Kerry Heads to Kiev after Russia's 'Declaration of War'

acaly ay. Ghr Mike wankam with us tonight, Mike, thank you. The fast-moving developments in ukraine.rs reports of two explo th crimean peninsula. Ofraat secretary of state John Ker nowing say. Kerry telling ABC news Russia's actions are a, quote, brazen act of aggression," an incredible act, and tonight the white house is considering all options. President Putin, however, defiant telling president Obama troec C oprusnter were ob but first abc'sef O correspry O ukr Reporter: David, all day L Russia tightened its grip here by sea the Russian Navy poured in more forces. On the roads, Russian troops were on the move. On the border between crimea and the rest of Ukraine, Russian soldiers were spotted digging trenches, a sign they're here to stay. And nearby in Russia itself, full-scale military exercises were underway ominously. For Ukraine's new prime minister, it was all too much. We are on the brink of the disaster. Reporter: In kiev, the Ukrainian government put its military on high alert and mobilized its forces for war. But Russia now totally controls this key part of Ukraine, the crimean peninsula, where there is strong popular support for Russia and where the Russian Navy has based ships for two centuries. Some of the local pro-russian forces took over government buildings and trashed them. At nato headquarters in Brussels, a sharp demand. Russia must stop its military activities and its threats. Reporter: But at the privolnoye Ukrainian military base here in crimea, that wasn't happening. Hundreds of Russian soldiers surrounded the base in utter silence. Why are you here? Just a few feet away behind the gate, Ukrainian soldiers. The Russian forces have demanded that they surrender their weapons. They've refused. You will stay here? No comment. But the wife of one of the Ukrainian soldiers now trapped in this eerie standoff, she is desperate. "We are hostages," she tells me, "The families, the kids, the wives were all worried about the orders that they will get from either side to shoot." It's horrible. As Russia ratchets up the pressure here, the danger is that the slightest spark, a panicked young soldier opening fire, a protester killed could touch off a major war. Nobody wants that but right now there is a sig any way out of this err, Ta I want to B ABC's chief global affairs correspondent Martha Raddatz tonight working her sources, as well. It seems a shift in tone with secretary Kerry O there have been so many warnings hurled at Russia duringis incredibly intense standoff, warnings that there will be consequences, there will be costs. On "This week," secretary ofstate John Kerry with very strong words for Vladimir putin.ussaged a military act of aggression against another country, and it has huge risks. It's a 19th century act in the 21st century. The president is currently considering all options. They're all on the table. All on the table and what more are we learning about that hour an half phone president Obama and president Putin? Reporter: He did spend 90 but that phone call, in fact, noneoseem Putin has sent I reinforcements. A senior administration official just a sh thatussiarec settling in so right now you have the Russians occupying crimea and what the U.S. And allies have done in response is to basically just cancel several meetings. There is talk of canceling the g-8 summit or kicking Russia out, but that does not seem to scare Vladimir Putin, David. At least not yet. Martha Raddatz, tonight, Martha, thank you.

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